Polymer electrolyte membrane fuel cells for vehicles are devices which generate electricity by electrochemical reaction between hydrogen and oxygen in the air and are well-known as environmentally friendly next-generation energy sources that have high electricity-generation efficiency and almost no exhaust materials, except for water. In addition, polymer electrolyte membrane fuel cells generally operate at a temperature of 95° C. or less and have high power density.
The reaction for electricity production by fuel cells occurs in a membrane-electrode assembly (MEA) which includes a perfluorinated sulfonic acid ionomer-based membrane and a pair of electrodes such as an anode and a cathode. Hydrogen supplied to an anode, which is an oxidation electrode for fuel cells, is split into a proton and an electron, and then the proton is moved through the membrane to a reduction electrode, that is, a cathode. As consequence, the electron is moved via an exterior circuit to the cathode. Then, at the cathode, an oxygen molecule, the proton and the electron react together, to produce electricity and heat, and at the same time, water (H2O) is produced as a by-product.
In general, hydrogen and oxygen in the air, which are reaction gases for fuel cells, crossover through the electrolyte membrane to facilitate production of hydrogen peroxide (HOOH). The hydrogen peroxide produces oxygen-containing radicals such as a hydroxyl radical (.OH) and a hydroperoxyl radical (.OOH). These radicals attack the perfluorinated sulfonic acid-based electrolyte membrane, inducing chemical degradation of the membrane, which finally has negative impact of reducing durability of fuel cells.
As a conventional technology to mitigate such chemical degradation of the electrolyte membrane, various kinds of antioxidants to the electrolyte membrane has been added.
For example, an antioxidant includes a primary antioxidant functioning as a radical scavenger, a secondary antioxidant functioning as a hydrogen peroxide decomposer or the like.
Examples of the primary antioxidant include cerium-based antioxidants such as cerium oxide and cerium (III) nitrate hexahydrate antioxidants, terephthalate-based antioxidants and the like. The secondary antioxidants include manganese-based antioxidants such as manganese oxide antioxidants.
However, as reported in the related arts, cerium oxide may have a problem that antioxidant activity is inversely proportional to long-term stability. There is an urgent need for research on novel antioxidants with both better antioxidant activity and excellent long-term stability.
The above information disclosed in this Background section is provided only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.